BEIJING — The United States called on China Thursday to allow peaceful protests, after Beijing police detained six foreigners amid a wave of demonstrations by pro-Tibet activists during the Olympics.

"We are concerned by recent reports that the Chinese have detained protesters," the embassy said in a statement.

"We call on China to respect the fundamental and universally recognised right of all persons to peacefully express their views, including Chinese citizens, and we urge the Chinese to put their best face forward during these Olympic Games."

The US statement came shortly after Beijing police said it had handed out 10-day detention terms to six foreigners believed by an overseas activist group to be pro-Tibet campaigners involved in Olympic protests this week.

In a brief faxed statement, the city police information department said "Thomas" and five other foreigners had been apprehended on Tuesday for "upsetting public order", without identifying the six people any further.

"Beijing police decided to give Thomas and the five others 10 days of administrative detention," the faxed statement said.

Administrative detention is a punishment that can be meted out by Chinese police without having to go through the courts.

A US embassy spokeswoman declined to comment on the report of the detention of the six and emphasised the statement was not in direct response to those cases.

But Students For a Free Tibet said it assumed the six were American pro-Tibet activists who police detained in Beijing on Tuesday.

"These young men were in Beijing to amplify Tibetan voices calling for freedom and human rights and the right of all people to freedom of expression," Students For a Free Tibet executive director Lhadon Tethong said.

"They are no more guilty of a crime than Tibetans or Chinese who speak out for justice.

"For the Chinese authorities to sentence them at all shows the government's paranoia and intolerance of even the most peaceful challenges to its control."

Students For a Free Tibet has orchestrated a series of protests in Beijing to coincide with the Olympics in an effort to highlight what it says is China's repressive 57-year rule of Tibet.

In comments published by French newspaper Le Monde on Thursday, exiled Tibetan spiritual leader the Dalai Lama said more than 400 people had been killed since Chinese security forces cracked down on unrest in Tibet in March.

At least eight pro-Tibet protests have taken place in Beijing since early August to coincide with the Olympics, which end on Sunday.

Most of the previous protesters were deported from the country after being held by police for a short time, with a total of 10 foreign activists currently still believed in police custody.

Aside from the six Americans picked up on Tuesday, two other Americans, a Tibetan-German and a Briton have been missing since trying to stage a protest near the Olympic venues just after midnight on Thursday.

Among the six detained on Tuesday was James Powderly, an American artist who planned to project a giant laser beam onto a Beijing building with a message in support of a free Tibet.